Sewage and water treatment technologies. Water treatment technologies. Drinking water purification methods

A standard reverse osmosis installation includes: a block of fine filters; Cartridge filters with five-micron cartridges are used; pump block high pressure; block of membrane modules; consists of rolled membrane elements enclosed in fiberglass or stainless steel housings; acid and inhibitor dosing unit to prevent membrane contamination by salt deposits (the need for acid and inhibitor dosing and doses are determined by calculation based on the value of the Langelier index of the concentrate); flushing unit - flushing is necessary to extend the service life of the membranes, because in any case, during operation, salts are deposited on their surface (the frequency of washing depends on the quality of the source water and the correct calculation of the installation and can be no more than once every three to four months). Additionally, in industrial installations, conductometers are installed to monitor the quality of permeate, an automation cabinet with a controller, and many other devices for automation and process control.

The productivity of reverse osmosis plants for permeate is on average 60-75%. Standard installations are limited to a working pressure of 16 bar, because... This is the maximum pressure for PVC pipes. The use of stainless pipes increases the cost of installation. When the salinity content is above 2000-3000 mg/l, the operating pressure becomes higher than 16 bar, and to reduce it, as a rule, the concentrate discharge is increased and the permeate productivity is correspondingly reduced. The selectivity of reverse osmosis membranes is from 98 to 99.7% for NaCl, operating pressure is from 6 to 25 bar.

Both chemical desalting and reverse osmosis make it possible to obtain water with a specific electrical conductivity of 5-50 µS/cm, depending on the salt content of the source water. Deeper desalting is carried out in two stages. Each installation, be it H-cationization, chemical desalting and especially reverse osmosis, must be calculated and selected individually for a specific case.

Corrective water treatment
Traditionally, the following are used for corrective water treatment: phosphates (trisodium phosphate, hexametaphosphate, tripolyphosphate and various mixtures thereof) to prevent the appearance of calcium scale and maintain the pH level of the water, which protects steel from corrosion; sodium sulfite for chemical deoxygenation of water after a deaerator or instead of a deaerator with a low flow rate of make-up water (up to 2 m3/h); ammonia for binding carbon dioxide in feed water and steam in order to protect the feed and steam-condensate ducts from carbon dioxide corrosion.

The use of these reagents requires special reagent facilities. Phosphates are first dissolved in a special solution tank, then the solution is filtered using a clarification filter to remove contaminants. When preparing a solution of sodium sulfite, it is necessary to take measures to isolate it from air. To dissolve sulfite, a sealed tank is used, which must be purged with steam before supplying water for dissolution. Special requirements apply to premises and qualifications service personnel when working with ammonia, which belongs to the class of hazardous substances. In addition, ammonia causes corrosion of copper-containing alloys. For small boiler houses (as opposed to thermal power plants), it is simply unrealistic to use traditional corrective water treatment technologies for the reasons listed above. There are two options left: not to carry out corrective treatment at all, reducing the operating efficiency and service life of the main equipment, or to use effective and easy-to-use modern reagents (albeit quite expensive), the costs of which may not be so high at low replenishment volumes. Modern reagents are supplied in liquid form, ready for use, and can be diluted with softened water in any proportions. When using them, no special reagent facilities are required; only a solution tank and a dispenser pump are sufficient.

> Water treatment systems

Today, the term “water treatment” is firmly established. Although this term first appeared with the advent of steam boilers and steam engines. Scientists have noticed that the durability of these structures directly depends on the quality of water. The water that was used in steam boilers and steam engines were prepared in a special way.

Water treatment is the process of removing all impurities from water, from suspended particles to metal salts.

We deal with water treatment every day. Why do auto parts stores sell distilled water? For battery maintenance. Because if you fill the battery ordinary water- in a few days you simply won’t start the car.

Nowadays, this term has become more widely understood. Domestic water treatment has been added to industrial water treatment. A huge number of household filters have appeared on the market. The environment is deteriorating, and people have noticed that our health depends on the purity of the water we consume.

Are water treatment and water purification synonymous?

At the household level, water treatment and water purification are one and the same. These are synonyms.

A filter for purifying water from iron is one of the elements of the system in a cottage or country private house.

A water softening filter is another element of water treatment.

Water treatment systems - main components

Let's look at the main components of the system:

1. Mechanical filter. It is usually used as a self-washing filter, where mechanical impurities are retained by a metal mesh. In cases with high turbidity, sediment filters are used, organized in columns of various sizes with sand backfill.
2. Iron filter. Serves to remove dissolved iron from water. At the same time, it removes manganese and hydrogen sulfide.
3. Filter softener. Removes hardness salts from water.
4. Carbon filter. Removes odor and retains particles of filter materials from previous filters. It can be implemented in the form of a cartridge filter or in the form of a column.
5. Filter-disinfectant based on an ultraviolet lamp. Removes bacteria in water. These filters are most relevant for wells and shallow wells.
6. Reverse osmosis filter. Removes fluoride and other impurities. Used for cooking drinking water.

The fifth point becomes the most relevant Lately. One neighbor cleans the drains and takes the purified water away, and the second neighbor behind a high fence pours it under himself without any treatment. So it turns out that there are no clean wells left in the near Moscow region. Almost all of them contain E. coli. And the number of such neighbors is not decreasing.

In one of the villages of a prestigious area of ​​the Moscow region, we discovered anthrax spores in the water. Further study of the topic revealed that in the 30s there was a cattle burial ground on this site. Such cases are extremely rare, but there are precedents.

It is noticed that soft water tastes less good. In holy springs, water hardness is 7 mEq/l. But such hardness spoils heating appliances, scale forms in the kettle, and hot water boilers quickly fail. Here comes the task of optimizing industrial water treatment and domestic water treatment.

For artesian waters of the Moscow region, water treatment is necessary. The average iron content is 3 mg/liter. This is quite enough to turn light-colored laundry red when washed.

Elements of water treatment and water purification systems

As noted, according to technology, water treatment elements can be reagent-free or reagent-free. Obviously, there is no need to restore anything in the cartridge filter. You just need to replace the cartridge element in time. And the softener filter uses a saturated salt solution. This technology is considered reagent technology.

Iron removal filters are also divided into reagent and non-reagent ones.

• Reagent filters use a solution of potassium permanganate or table salt.
• In reagent-free - only air, which is supplied to the system by a compressor (although it is more correct to assume that in this case the reagent is air).

Water treatment begins with chemical analysis of water

The choice of certain technologies in water treatment depends on the chemical analysis of water. For example, when the pH value is less than 7 units, purification with aeration from iron is not used. Here it is necessary to install a pH corrector, or use ion exchange resins as a filter element.

Therefore, if you feel the strength and knowledge to install a water treatment system yourself, we strongly recommend that you contact a water treatment chemist to select a technological scheme. There are quite a lot of nuances.

City water also undergoes water treatment. Water disinfection on an industrial scale is carried out with chlorine. Most household filters are designed to remove chlorine.

Since all water treatment processes are hidden from our eyes, many scammers have appeared who, for very reasonable money, offer filters that will not only remove all harmful impurities from the water, but also charge the water with miraculous ions, without which it is generally impossible to live.

Water treatment system and its cost

Alas, miracles do not happen. The higher the degree of water purification, the more expensive the water treatment system is. The more productive the system, the more expensive it is.

It should be noted that there is a steady trend of constant reduction in prices for water treatment systems while improving the quality of their work. Science does not stand still. And membrane technologies entered water treatment technology in the form of reverse-somatic filters.

1. What is meant by the steam-water cycle of boiler plants

The steam-water cycle is the period of time during which water turns into steam and this period is repeated many times.

For reliable and safe work boiler important has water circulation in it - its continuous movement in the liquid mixture along a certain closed circuit. As a result, intensive heat removal from the heating surface is ensured and local stagnation of steam and gas is eliminated, which protects the heating surface from unacceptable overheating, corrosion and prevents boiler failure. Circulation in boilers can be natural or forced (artificial), created using pumps.

In modern boiler designs, the heating surface is made of separate bundles of pipes connected to drums and collectors, which form a sufficient complex system closed circulation circuits.

In Fig. A diagram of the so-called circulation circuit is shown. Water is poured into the vessel, and the left wheel of the U-shaped tube is heated, steam is formed; specific gravity the mixture of steam and water will be less compared to the specific gravity in the right knee. The liquid in such conditions will not be in a state of equilibrium. For example, A - And the pressure on the left will be less than on the right - a movement begins, which is called circulation. Steam will be released from the evaporation mirror, further removed from the vessel, and feed water will flow into it in the same amount by weight.

To calculate circulation, two equations are solved. The first expresses the material balance, the second the balance of forces.

The first equation is formulated as follows:

G under =G op kg/sec, (170)

Where G under is the amount of water and steam moving in the lifting part of the circuit, in kg/sec;

G op - the amount of water moving in the lower part, in kg/sec.

The balance of forces equation can be expressed by the following relationship:

N = ∆ρ kg/m 2, (171)

where N is the total driving pressure equal to h(γ in - γ cm), in kg;

∆ρ – the sum of hydraulic resistance in kg/m2, including the force of inertia, arising when the steam-water emulsion and water move through the office and ultimately causing uniform movement at a certain speed.

The boiler circulation circuit contains a large number of pipes operating in parallel, and their operating conditions cannot be completely identical for a number of reasons. In order to ensure uninterrupted circulation in all pipes of parallel operating circuits and not cause circulation overturning in any of them, it is necessary to increase the speed of water movement along the circuit, which is ensured by a certain circulation ratio K.

Typically, the circulation ratio is selected in the range of 10 - 50 and, with a low heat load of the pipes, much more than 200 - 300.

The water flow in the circuit, taking into account the circulation rate, is equal to

where D = steam (feedwater) flow rate of the calculated circuit in kg/hour.

The speed of water at the entrance to the lifting part of the circuit can be determined from the equality

2. Reasons for the formation of deposits in heat exchangers

Various impurities contained in heated and evaporated water can be released into the solid phase on internal surfaces steam generators, evaporators, steam converters and condensers steam turbines in the form of scale, and inside the water mass - in the form of suspended sludge. However, it is impossible to draw a clear boundary between scale and sludge, since substances deposited on the heating surface in the form of scale can turn into sludge over time and vice versa; under certain conditions, sludge can stick to the heating surface, forming scale.

Of the elements of the steam generator, heated screen pipes are most susceptible to contamination of internal surfaces. The formation of deposits on the internal surfaces of steam-generating pipes entails a deterioration in heat transfer and, as a consequence, dangerous overheating of the pipe metal.

The radiation heating surfaces of modern steam generators are intensively heated by a combustion torch. The heat flow density in them reaches 600–700 kW/m2, and local heat flows can be even higher. Therefore, even a short-term deterioration in the heat transfer coefficient from the wall to boiling water leads to such a significant increase in the temperature of the pipe wall (500–600 °C and above) that the strength of the metal may not be sufficient to withstand the stresses that arise in it. The consequence of this is metal damage, characterized by the appearance of holes, lead, and often pipe rupture.

During sharp temperature fluctuations in the walls of the steam-generating pipes, which can occur during the operation of the steam generator, scale peels off from the walls in the form of fragile and dense scales, which are carried by the flow of circulating water to places with slow circulation. There they settle in the form of a random accumulation of pieces of various sizes and shapes, cemented by sludge into more or less dense formations. If a drum-type steam generator has horizontal or slightly inclined sections of steam-generating pipes with sluggish circulation, then deposits of loose sludge usually accumulate in them. A narrowing of the cross-section for the passage of water or complete blockage of steam-generating pipes leads to circulation problems. In the so-called transition zone of a direct-flow steam generator, up to critical pressure, where the last remaining moisture evaporates and the steam is slightly overheated, deposits of calcium, magnesium compounds and corrosion products are formed.

Since a direct-flow steam generator is an effective trap for sparingly soluble compounds of calcium, magnesium, iron and copper. If their content in the feed water is high, they quickly accumulate in the pipe part, which significantly reduces the duration of the steam generator’s operating campaign.

In order to ensure minimal deposits both in the zones of maximum thermal loads of steam-generating pipes, as well as in the flow path of turbines, it is necessary to strictly maintain operational standards for the permissible content of certain impurities in the feed water. For this purpose, additional feed water is subjected to deep chemical purification or distillation in water treatment plants.

Improving the quality of condensates and feed water significantly weakens the process of formation of operational deposits on the surface of steam power equipment, but does not completely eliminate it. Therefore, in order to ensure proper cleanliness of the heating surface, it is necessary, along with one-time pre-start cleaning, to also carry out periodic operational cleaning of the main and auxiliary equipment, and not only in the presence of systematic gross violations of the established water regime and insufficient effectiveness of the anti-corrosion measures carried out at thermal power plants, but also in conditions of normal operation of thermal power plants. Conducting operational cleaning is especially necessary at power units with direct-flow steam generators.

3. Describe the corrosion of steam boilers along the steam-water and gas paths

Metals and alloys used for the manufacture of thermal power equipment have the ability to interact with the environment in contact with them (water, steam, gases) containing certain corrosive impurities (oxygen, carbonic and other acids, alkalis, etc.).

Essential for disrupting the normal operation of a steam boiler is the interaction of substances dissolved in water with washing it with metal, resulting in destruction of the metal, which, at certain sizes, leads to accidents and failure of individual elements of the boiler. Such destruction of metal environment called corrosion. Corrosion always starts from the surface of the metal and gradually spreads deeper.

Currently, there are two main groups of corrosion phenomena: chemical and electrochemical corrosion.

Chemical corrosion refers to the destruction of metal as a result of its direct chemical interaction with the environment. In the heat and power industry, examples of chemical corrosion are: oxidation of the outer heating surface by hot flue gases, corrosion of steel by overheated steam (so-called steam-water corrosion), corrosion of metal by lubricants, etc.

Electrochemical corrosion, as its name indicates, is associated not only with chemical processes, but also with the movement of electrons in interacting media, i.e. with the advent electric current. These processes occur when the metal interacts with electrolyte solutions, which takes place in a steam boiler in which boiler water circulates, which is a solution of salts and alkalis that have disintegrated into ions. Electrochemical corrosion also occurs when the metal comes into contact with air (at normal temperature), which always contains water vapor, which condenses on the surface of the metal in the form of a thin film of moisture, creating conditions for electrochemical corrosion to occur.

The destruction of a metal begins, essentially, with the dissolution of iron, which consists in the fact that the iron atoms lose some of their electrons, leaving them in the metal, and thus turn into positively charged iron ions, turning into water solution. This process does not occur uniformly over the entire surface of the metal washed with water. The fact is that chemically pure metals are usually not strong enough and therefore their alloys with other substances are used in technology. As is known, cast iron and steel are alloys of iron and carbon. In addition, silicon, manganese, chromium, nickel, etc. are added to the steel structure in small quantities to improve its quality.

Section two.

environmental assessment

2.2.1. Water clarification and coagulation

A feature of domestic water treatment plants (WPU) is that, as a rule, water from surface reservoirs is used as source water for them. Natural water contaminated with technogenic impurities contains a large amount of mineral impurities, suspended and organic substances.

Section two. PROTECTION OF THE WATER BASIN FROM DISCHARGES

2.2. Modern technologies water treatment at thermal power plants and their environmental assessment

2.2.2. Ion exchange desaltingBoiler make-up water

Shishchenko V.V., VNIPIenergoprom Institute; Fedoseev B.S., JSC "VTI"

In our country, the preparation of demineralized water for thermal power plant boilers and other technological purposes is carried out mainly using ion exchange technologies, including two or three stages of cation and anion filters. Experience in the use of ion exchange technologies spans more than 60 years. Currently, the development of ion exchange technologies and increasing the efficiency of ion exchange installations are carried out in the direction of improving the designs of ion exchange filters designed for countercurrent ionization and improving the quality and properties of ion exchangers for water treatment.

Section two. PROTECTION OF THE WATER BASIN FROM DISCHARGES

2.2. Modern water treatment technologies at thermal power plants and their environmental assessment

2.2.3. Thermal preparation technologyadditional water for make-upenergy boilers

Sedlov A.S., Moscow Power Engineering Institute (TU); Shishchenko V.V., VNIPIenergoprom Institute; Fedoseev B.S., JSC "VTI"

Thermal preparation technology is based on water distillation. In one apparatus - the evaporator - the water evaporates, in the other - the condenser - it condenses. In the evaporator, a minimum amount of salts supplied with the source water enters the steam. In addition, steam before entering the condenser using special devices cleared of impurities. The quality of the distillate formed in the condenser meets the quality standards for makeup water for ultra-high pressure power boilers.

Section two. PROTECTION OF THE WATER BASIN FROM DISCHARGES

2.2. Modern water treatment technologies at thermal power plants and their environmental assessment

2.2.4. Reverse osmosiswater desalination

Shishchenko V.V., VNIPIenergoprom Institute; Fedoseev B.S., JSC "VTI"

IN last years In the domestic practice of water desalination, there is an increased interest in reverse osmosis technology. Constructed and successfully operated whole line reverse osmosis units (ROU): at CHPP-23 of Mosenergo OJSC (developed by VNIIAM, capacity 50 m 3 /h, reverse osmosis membranes supplied by DOW Chemical); at the Nizhnekamsk CHPP (development and supply by Hidronoutics, productivity 166 m 3 / h).

Section two. PROTECTION OF THE WATER BASIN FROM DISCHARGES

2.2. Modern water treatment technologies at thermal power plants and their environmental assessment

Soft water means not only the absence of scale, but also an increased service life of equipment and a reduction in the development of corrosion.

If we describe new water treatment technologies, they can be divided into:

1. clarification - coagulation, settling, filtration;

2. water softening;

3. distillation or removal of salts;

4. degassing (thermal or chemical);

5. elimination of odors.

To better understand why this or that equipment is used in water treatment, it is necessary to consider in detail the stages of water treatment. The filters that can be used will also be considered.

Primary mechanical purification involves purifying water from mechanical and solid impurities. There is a mechanical filter with three-stage cleaning. At this stage, the water is cleared of all kinds of inclusions visible to the naked eye. After this stage, we already have purified water, but still with dissolved impurities.

All possible new technologies that come next may vary. That is, either one of them can stand, or they can follow each other. This is the so-called new method And new technology water treatment This may include deferrization, disinfection, degassing, descaling tablets, etc.

Deferrization

The main sources of iron compounds in natural waters are the processes of weathering, soil erosion and rock dissolution. Significant amounts of iron come from underground runoff and wastewater industrial enterprises. Iron may also be present in drinking water due to the use of iron-containing coagulants at municipal water treatment plants, which are used to clarify incoming water, or due to corrosion of water pipes.

Iron compounds can be found in natural water in a dissolved, colloidal and suspended state depending on the valency: Fe+2, Fe+3, as well as in the form of various chemical compounds. For example, ferrous iron (Fe+2) is almost always found in dissolved state in water, and ferric iron (Fe+3) - iron hydroxide Fe(OH)3 is insoluble in water, except in the case of very low pH values. There is another form of iron present in natural water - organic iron. It is found in water in different forms and as part of various complexes. Organic compounds iron is usually soluble or has a colloidal structure and is very difficult to remove. Colloidal particles, due to their small size and high surface charge, which does not allow the particles to approach each other and prevents their enlargement, preventing the formation of conglomerates, create suspensions in water and do not settle, being in a suspended state and thereby causing the turbidity of the source water.

One of modern trends non-chemical purification of groundwater is a biological method that is based on the use of microorganisms. The most common among them are iron bacteria. These bacteria convert ferrous iron (Fe2+) into oxide iron (rust Fe3+). These bacteria themselves do not pose a danger to the human body, but their metabolic products are toxic.

Modern biotechnologies are based on the use of the properties of a catalytic film formed on a sand-gravel load or on other similar finely porous material, for example, a column of activated coconut carbon, various synthetic materials, as well as on the ability of those same iron bacteria to ensure the course of complex chemical reactions without any energy costs and reagent use. These processes are natural and based on the biological laws of nature itself. Abundant development of iron bacteria is observed in water with an iron content of 10 to 30 mg/l, however, as experience shows, their development is possible even at an iron concentration one hundred times lower. The only condition is to maintain the acidity of the environment at a sufficiently low level with simultaneous access of oxygen from the air, at least in a negligible amount.

The final stage of biological deferrization is sorption purification to retain waste products of iron bacteria and the final disinfection of water with bactericidal rays. For all its advantages (for example, environmental friendliness) and prospects, biorefinery has only one drawback - the relatively low speed of the process. This, in particular, means that to ensure high productivity, large dimensions of capacitive structures are required. Therefore, oxidative and ion-exchange methods of iron removal are widely used.

Oxidative methods of deferrization involve the use of oxidizing agents such as air, chlorine, ozone, potassium permanganate, etc. to accelerate the reaction of converting the ferrous form of iron into the oxide form with further accelerated sedimentation of iron flakes by adding special chemicals - coagulants on sediment filters. This technology is mainly applicable to large municipal systems.

Ion exchange as a method of water treatment has been known for quite a long time and is mainly used to soften water. Previously, natural ion exchangers (sulfonated carbons, zeolites) were used to implement this method. However, with the advent of synthetic ion exchange resins, the efficiency of using ion exchange for water treatment purposes has increased dramatically.